The invention relates to a spotting and picking processes using pin heads, and to robotic apparatuses for carrying out such processes using pin heads.
Microarraying is a technique in widespread use. Conventional microarraying is based on standard multi-well plates having a 4.5 mm grid and 384 wells, although other sizes are available. Liquid samples are stored in the wells of a well plate. The liquid may be assays or any other biological or chemical sample of interest. Sub-samples of the liquid within the well plates are carried to and deposited on a spotting surface, typically microscope slides, as required. Usually many such deposits are needed and microarraying is a process whereby multiple deposits can be made simultaneously and under machine automation.
FIG. 1 shows a typical microarraying robot highly schematically in plan view. The robot comprises a main bed 10 onto which well plates 4 are delivered by an automated well plate feeder 6 with a number of delivery lanes (two in the illustration) through a delidding/relidding mechanism (not shown). Each delivery lane has a feed port 7 and a restack port 8 where well plates are stacked before and after visiting the main bed 10 respectively.
The process of microarraying is one of spotting the liquid from the well plates 4 onto spotting surfaces provided by the microscope slides 2 which are also arranged on the main bed 10. This process is carried out by a pin head 12 which is moved around the robot by x- y- and z-positioners 14, 16 and 18 respectively. The pin head 12 is carried by the z-positioner, which is in turn carried by the y-positioner, which is carried by the x-positioner. These items are shown schematically with dashed lines. The pins of the pin head can be pneumatically actuated between retracted and extended positions. The process of pneumatically actuating the pins into the extended position is referred to as “firing” and is the process used to deposit liquid from the pins onto the spotting surface.
In operation, the head 12 is initially positioned so as to align its pins with the required section of one of the well plates 4. The head 12 is then actuated so as to partially immerse the pins in the liquid to be spotted. Surface tension ensures that samples of fluid remain on the pins as they are lifted away from the well plate. The pin holder is then carried by the head 12 to a chosen location above one of the microscope slides 2 for spotting where the pins are fired downwards to deposit the carried fluid at the chosen location. The liquid is deposited in a set pattern of many closely spaced spottings. One or more dense grids of spottings is usually generated by each pin. Dense spot grids, typically 11×11 squares, are generated with a 4.5 mm separation between adjacent grids.
After one round of spotting, the pin head needs to be cleaned before the pins can be used to pick up another group of samples from the well plates. For cleaning, the robot is provided with a washing station 20 and a drying station 24 which are usually arranged adjacent to each other for convenience. The washing station 20 is illustrated as including first, second and third baths 21, 22 and 23. The drying station 24 also includes halogen lamps 26 to assist drying by heating the pins.
After completion of a spotting run, the x- y- and z-positioners 14, 16 and 18 move the head over to the washing station 20. The pins are actuated into their extended positions and dipped into the first wash bath 21, containing water for example. The first bath 21 may be fitted with upstanding brushes immersed in the water, in which case the x- and y-positioners are used to move the pins over the brushes in a rotary motion in the xy-plane. The head is then moved to the second bath 22, which also contains water for further cleaning, and may also include bleach. The head is then moved to the third and last bath 23, which contains ethanol for more cleaning. Ethanol is used in the last bath 23 in view of its volatility which assists the subsequent drying of the pins. It will be appreciated that the named cleansing agents are mentioned to give concrete examples. Other cleansing agents are sometimes used.
The pin head then leaves the washing station 20 and is moved over to above the drying station 24. The halogen lamps 26 are switched on to heat the pins. An air blower is then switched on to cool the pins to ambient temperature.
The pin head 12 is now clean and ready to proceed with further spotting, so is moved over to the target well plate to pick up further liquid and the microarraying process repeats.
Colony picking uses similar apparatus to spotting, but may be considered to be the reverse process in which a pin head is used to move samples from a colony-bearing surface to a well plate. Namely, pins of a pin head are used to pick up samples from colonies and deposit them in a liquid held in wells of well plates. The colonies are provided in petri-dishes, Q-trays or omni-trays for example. Once all the pins have been used, they need to be cleaned before further inoculation to avoid cross-contamination using a similar washing and drying process to that described above for micro arraying.
The speed of picking and spotting processes is often limited significantly by the duration of the the washing and drying steps. The washing and drying steps are critical in biological applications as cross-contamination due to “carry-over” can often be a problem, so should not be compromised. The conventional way of increasing throughput of the robots is thus to increase the speed and/or acceleration of the drives used for the x- y- and z-positioners. However, this poses increased constraints upon the construction of the equipment and generally requires a disproportionate increase in cost.